This proposal is a competing continuation application to extend the work of R01 MH56888, now titled "Interpersonal Functioning and Emotion in Borderline Personality." The primary goal of the work has been the detailed assessment of interpersonal functioning in borderline personality disorder (BPD) at multiple levels of resolution (adult attachment styles, functioning in major social domains, daily social interaction, and social cognition). We propose to focus this work more explicitly on the general hypothesis that many of the interpersonal features of BPD arise through maladaptive functioning of the attachment system. Since attachment theory is best understood as a theory of interpersonal relatedness and its relationship to emotion regulation, we have also added new measures of emotional reactivity and regulation. Our first specific aim is to investigate the hypothesis that many of the interpersonal behaviors of persons with BPD can be understood as frustrated (and frustrating) bids for attachment. To investigate hypothesized links between BPD, disruptions in attachment, and problems in emotional reactivity and regulation, our second specific aim is to supplement our current evaluations with psychophysiological assessments (pupillometry) of the dynamic time course of emotional information processing. Our third specific aim is to do repeated longitudinal assessment of attachment, interpersonal functioning, and emotion regulation over a one-year period at quarterly intervals in order to examine the trajectories they display and to explore their reciprocal influences. The work will be done with a sample of 168 participants aged 21 to 60 receiving a multimodal assessment battery including clinical interviews, self-report questionnaires, psychophysiological assessments, consensus diagnostic conferences, and information collected from up to three informants. We have expanded our sampling frame to capture the full spectrum of BPD severity using three strata (0-2, 3-4, and 5 or more diagnostic criteria) in two groups (psychiatric patients and community residents). The work will reveal important mechanisms in adults underlying attachment, interpersonal functioning, emotion regulation, and the relationships between these constructs. The identification of such mechanisms is the best way forward to improved, evidence-based treatments that can address impairments in interpersonal functioning and emotion regulation in BPD at the level of day-to-day behavior.